Tektronics 2213A deflection problem...?

[rayyolanda]

Hi guys, hope you can help me on this prob.

I have a Tek 2213A scope. i turned it on the other day for thefirst time in a while and all was ok. Then I heard a buz and higher pitch from the power supply. After this the scope only seems to display the trace in about 80% of the screen in both X and Y scales....so the trace is shrunk by about 20%, but it does seem to be correct otherwise, trigger etc all ok.

I can not adjust this. I have looked at the manual but the one that I have is for later scopes and is a little different. I am guessing this is a high voltage problem. How do I check this and which components are likely suspects.

Thanks in adavance.......
Ray

 

[BrownOut]

I doubt it's a high voltage problem. More than likely, it's a horizontal amplifier problem. Best to get a correct manual and probe the horizontal circuit and compare the amplitude of the signal with the manual. Tek scopes can have great service manuals with the levels of critical signals listed. Try the web for a manual. I found one for my tek scope and downloaded it for free.

 

[rayyolanda]

Thanks for the reply. the reason I did not think it was a horizontal prob was that the trace seems to be compressed by 20% also.....I will do as you suggest and look for another manual and probe the horz section. Any other clues ....please let me know.....cro / tv..is really not my thing so I am learning a bit here.

 

[BrownOut]

While you're probing the horz circuit, check the DC voltages on the amplifiers. If they are low, that would cause the symptoms.

 

[crutschow]

Could be a bad electrolytic capacitor overloading the power supply, causing low voltages to the amplifiers. Electrolytics are the component most likely to fail in an old electronic device, especially one that isn't used very often.

 

[rayyolanda]

Thanks guys.
The low volts are in spec, -8.6 was -8.37 but I adjusted it and all others are still in spec 102.7, -8.6, 8.67, 30.36 and 5.15.
I think BrownOut is correct and this is a Horizontal problem. I can move the trace vertical all the way off screen but the horizontal starts 10% in and finishes 10% short.
BTW, all the controls seem to work fine even Calibrate, just not enough for this problem. The power supply is still noisey.

 

[ljcox]

You can download manuals from the Boat Anchor site.

 

[rayyolanda]

Hi guys, a bit of an update on my investigations.
I believe the problem is with the -8.6 volt supply. It sometimes drops to about -7.9 and is unstable to adjust with the power supply dropping down (up really) when close to -8.5.
Also, according to the manual the resistance should be about 114 ohms to ground....it is about 85. I isolated the main supply by pulling up a link so I know that main is ok.
I am search around trying to find the source of this low resistance but the manual I have is for a 1981 model. I have a 1984 scope.

Does anyone have a manual for this model?

The one I have is very similar but there are many differences and component numbering, locations and boards are all different.

Thanks......Ray

 

[ljcox]

Does anyone have a manual for this model?

Thanks......Ray

Ray,
Did a search for the Boat Anchor site that I menyioned yesterday and found it.
https://bama.edebris.com/manuals/
but it is out for repair.

I was able to download the manual for my Tektronics scope & the manual for one of the plug ins.

 

[rayyolanda]

Hi Len, thanks for the link. That manual is the one that I have. Unfortunately it is not the exact same model.

 

[ljcox]

Hi Len, thanks for the link. That manual is the one that I have. Unfortunately it is not the exact same model.

Ray,
You're welcome.

However, I'm confused by your post.

The link has many Tek scope manuals.

But your post reads as though there was only one model at the site.

 

[rayyolanda]

Len, sorry if I have been a bit confusing. I downloaded the 2213A and 2213 files which are a service manual and an operation guide. I even downloaded th 2215 to see if it might have the boards the same as mine, no luck..

My 2213A has a vertical / attenuator board and a separate horizontal sweep board, but the manual has a single board for these functions. The circuit is very similar but component names change and the board layouts are different. It just makes it hard to trace the circuit. There must be another version of the manual.

I am still trying to track down the low resistance on the -8.6 volt and hopefully that will fix the problem. Although I am not totally convinced about this because when I had the -8.6 adjusted ok the fault still existed.......this does not mean of course that a component is still not defective and causing this.

Thanks for your interest in my problem, I was hoping that someone had seen it before.

Ray

 

[ljcox]

Ray,
Now I understand your problem.

If you think there is a faulty component that is taking excessive current, you may be able to locate it using a modern version of a very old technique that was used in electromechanical telephone exchanges to locate a short circuit in a wiring multiple as illustrated in the attachment.

It was called the “Drop of Potential Test” (DoPT). The situation faced by a technician was this:- he has to locate a short between 2 tags in a wiring multiple where there are 600 wires multipled over 10 switch banks.

It was a formidable task to find a S/C in this nightmare. Although you can remove the switches and thus see the contacts, the soldered connections are on the other side and are invisible due to the wiring multiple. Disturbance to the wiring form (to find the fault visually) was to be avoided as it could cause extra faults. And it would be very time consuming.

So someone invented the DoPT. As you can see in the attachment, a current was created using the exchange battery and an incandescent lamp. The technician then used a pair of 1 Ohm earphones to detect the current.

Starting at the terminal strip, he would connect the earphones across a0 & a1, then a1 & a2, etc until no click was heard.

Thus the wiring form had to only be disturbed at the fault site.

So you could possibly do this on a PCB using a multimeter set to the millivolt range and measure the voltage between each point until the fault is located. It is more complicated than the exchange situation as the PCB track lengths will vary between the components and the track may change in width. Also, there will be a legitimate current in the track.

But if the fault current is large enough, then it should be possible.

 

[rayyolanda]

Len, thanks for that....I think I will pull up links or components to try to see when the resistance goes up. This is only a theory I have developed to explain the problem....it may not be the cause. The only thing I can see wrong is the dropping of the -8.6, well raising really as it gets closer to 0v due to low er that normal resistance. I am a little time poor at the moment but I will try to find some time to look into it more...
Thanks again
Ray

 

[rayyolanda]

Hi Everyone,

OK, I have not had much time to work on this problem but I noticed a strange
symptom. I selected x-y mode so that I could move the dot around and measure
the deflection voltages.

What I see is that the dot is like two dots about 3 divisions apart with a
baseline between them. When I control the <position> it moves
horizontally...all OK. When I control the Chan 2 position it moves up and
down...OK. But when I control the Chan 1 position it moves horizontally not
vertically... and it moves opposite to the control direction...rotate right and
the trace moves left....rotate left and the trace moves right.

Any ideas?

Thanks....Ray

 

[ljcox]

Ray,
You may have 2 problems or it may be different symptions of the same problem.

I don't know about the Ch 1 position control issue, it is presumably due to some connection between Ch1 & the Horiz amp - either through one of the supply rails or a short somewhere. What is common between Ch1 & the H amp?

The Horizontal line sounds to me like a signal of some sort in the H amp eg. excessive ripple on one of the supply rails.

You could apply a sinewave signal (ideally it should be a sawtooth) to Ch 2 and see what the effect is.

If it is mains hum, it should produce a stable pattern when the input frequency is 60 Hz (assuming your mains is 60 Hz) or multiples thereof.

If you can generate a sawtooth, you should be able to see the shape of the signal.

Can you borrow another scope from someone? This would be a valuable aid.

Hope this helps.

 

[rayyolanda]

Thanks Len.
I think my original problem is something to do with sweep generation / horizontal timing. Both CH1 and CH2 are affected the same..both short traces start and stop exactly the same time. Not sure what is the common points between CH1 and H amp....maybe this is symptomatic of being in XY mode....?
If this was hum or ripple I would expect to see some jitter at start and end of the trace but it is rock steady...it really seems like a timing issue.
No scope to borrow at the moment.....oh I am in NSW, Central Coast.
Ray

 

[ljcox]

Thanks Len. You're welcome.
I think my original problem is something to do with sweep generation / horizontal timing. Both CH1 and CH2 are affected the same..both short traces start and stop exactly the same time. I assume you're talking here about the effect in the normal mode, not the XY mode. Not sure what is the common points between CH1 and H amp....maybe this is symptomatic of being in XY mode....?
If this was hum or ripple I would expect to see some jitter at start and end of the trace but it is rock steady...it really seems like a timing issue. I disagree, see below.
No scope to borrow at the moment.....oh I am in NSW, Central Coast. That's about 1500 km too far north to borrow mine.
Ray

The line you see on the screen in the XY mode indicates to me (as I said previously) that a signal of some kind is getting into the H amp.
The most likely is ripple particularily given that you said in your first post that you hear a buzz from the PS.
I don't see why there would be jitter at the start or end of the trace.
I would expect that ripple would show as a smooth line possibly with dots at each end due to the spot dwelling there as it reverses. eg. if it were a sine signal, the spot would move slowest at the point where its direction is reversing, ie. at the top and bottom of the waveform.

What happens if you inject some 50 Hz signal into CH1 and then Ch2? You could probably do this simply by setting the Ch1 & 2 attenuators at say 100 mV/cm and put your finger on the probe tip.

After breakfast, I'll have a look at my Tektronics cro. That may give me more inspiration.

 

[ljcox]

Ray,
I had a look at my Tektronics CRO but I can't see any X-Y function.

But my old HP scope has one. The X signal is input to ChA and the Y to ChB.

So I assume that your's is the same. This would explain why you said that moving the Ch 1 position moves the display horizontally (this had me puzzled originally & is the reason I asked in my 20 April post - what is common between the Ch1 & H amps?).

So the signal that is causing the line in the XY mode may be due to a signal (eg. due to excessive ripple) in the Ch1 amp.

The reason I suspect ripple is because you said the PS started to buzz. A problem in the PS is likely to increse the ripple on some or all supply rails.

Have you considered using the cro to analyse itself?

That's what I did to find a fault in the HP (before I had the Tektronics one which is on loan from a friend).

I don't recall the fault that was in the HP (it has had several faults in the time I've had it) but it was working enough for me to look at some of the waveforms inside it and to deduce what the fault was.

In your case, you said that both Ch1 & 2 work (in the normal mode) except that their traces are only about 80% of the norm.

So you should be able to look at the power rails to see if there is ripple &, if so, track down the cause.

 

[rayyolanda]

Hi Len,
Thanks again for your replies and interest. I looked at the power rails...the 100V has the most ripple but it is only 60mV the others are 10 to 20mV. A lot of people seem to suggest the PS filter caps......maybe I should just swap them out.
I am getting a manual for the scope...soon I hope.....I have been using the 2215A manual which is very similar but different in key areas.
Ray